It is well-established that opiate abuse causes difficult management problems in the fetus and neonate. More subtle defects of the central nervous system which might be caused by exposure of the fetus to opioids are predictable but have never been subjected to systematic morphological analysis coupled with behavioral evaluation in the fetus. The time of onset of analgesia and dependence will be determined by observing the effects of opioids and withdrawal on spontaneous and reflex activity in utero. This will be correlated with the state of neural development. Using binding studies and autoradiography opiate receptors will be located in the fetal spinal cord. This information will be correlated with the state of cellular and subcellular development. One segment of substantia gelatinosa of animals chronically exposed to morphine will be examined for the following: size; neuron size and number; length, size and spine density of processes; neuron/glia ratios; and total cell number. The ultrastructural profile of substantia gelatinosa of morphine-dependent fetuses will be compared with that of normal animals. These experiments will provide two types of information: the state of the nervous system when opioids become effective and the morphological changes caused by chronic exposure to opioids during development.